Diesel engines are often used to power various types of work machines. Despite various improvements made over the years to the diesel engines, diesel engines still remain not only a source of vibration and noise, but also undesirable emissions, such as carbon dioxide (CO2), nitrogen oxides (NOx), unburned hydrocarbons and soot. All of these have been found to contribute to global warming and air pollution.
Over the years, engineers have attempted to decrease the use of diesel engines in order to decrease undesirable emissions, along with noise and vibrations. For instance, work machines often use a diesel engine to power a hydraulic pump that delivers hydraulic fluid to a hydraulic cylinder. Movement of a weight-driven plunger within the hydraulic cylinder drives the movement of the work machine's implement, such as a loader, excavator, or the like. When the plunger is retracting under the load of the weight, some of the hydraulic power created by the hydraulic fluid being pushed from a decreasing volume of the cylinder below the retracting plunger can be captured and re-used. The hydraulic fluid being pushed out of the cylinder can flow to an increasing volume within the cylinder above the retracting plunger. Thus, during retraction, some of the energy created by the hydraulic flow can be recovered, and the hydraulic fluid flow from the pump can be decreased, thereby also decreasing the diesel engine power required to operate the pump.
Due to an area of a rod that couples the plunger to the weight, the expanding volume above the retracting plunger within the cylinder is often smaller than the decreasing volume below the retracting plunger. Thus, during plunger retraction, more fluid is being pushed from the decreasing volume below the plunger than is needed to fill the increasing volume above the plunger. A throttle valve is used to bleed the excess hydraulic fluid flowing from the decreasing volume of the cylinder to a hydraulic fluid tank. Thus, only approximately half of the hydraulic fluid flowing from the decreasing volume below the plunger is delivered to the increasing volume above the plunger. Because of the significant amount of high pressure hydraulic flow being bled from the power system, the rate of energy recovery is too low to be efficient. In addition, the energy recovery only occurs when the plunger is retracting within the cylinder, thereby further reducing the efficiency of the energy recovery.
In order to increase the energy recovery, engineers have found methods of storing the captured energy from the pressurized hydraulic flow caused by plunger retraction. For instance, Patent Abstracts of Japan 2002-195218, which was published Jul. 10, 2002, shows that the excess flow of hydraulic fluid being bled to the fluid tank from the decreasing volume below the retracting plunger can also be used to operate a turbine that powers a generator. Electric current generated by the generator can be delivered to a water reservoir, in which electrolysis separates the water into hydrogen and oxygen. The hydrogen can be accumulated and stored in a hydrogen absorbing alloy cell. When needed, the hydrogen gas can be supplemented with hydrogen created in a reformer and delivered to a fuel cell, in which the hydrogen is re-combined with the oxygen to produce heated water and electric current. The electric current is delivered to an electric motor that powers the hydraulic pump. Thus, the diesel engine can be replaced with the electric motor ultimately driven partly by the recovered hydraulic power, thereby even further reducing undesirable emissions, noise, and vibrations, and increasing the efficiency of the energy recovery.
Although the electric motor powered by the fuel cell does decrease undesirable emissions, noise and vibrations, there is still room for improvement. Even with the use of the electric motor, the excess hydraulic flow from the decreasing volume of the cylinder to the fluid tank is throttled by the throttle valve prior to powering the turbine. Thus, some of the hydraulic power of the flow is wasted, rather than used to power the generator. Moreover, fuel cells, hydrogen absorbing alloys cells and reformers can be relatively expensive and problematic.
The present invention is directed to overcoming one or more of the problems set forth above.